Voltage regulators are circuits designed to deliver a constant output voltage despite changes in load, temperature, and/or power supply. A switching regulator is a type of voltage regulator that produces a constant output voltage by alternately connecting and disconnecting an input voltage.
Switching regulators are becoming increasingly popular because of their efficiency, size, and weight. In addition, switching regulators, unlike linear regulators, can provide an output voltage that is higher or lower than the input voltage. A switching regulator that generates a reduced output voltage is usually referred to as a “buck” regulator and a switching regulator that generates an increased output voltage is usually referred to as a “boost” regulator. There are also other kinds of switching regulators, such as a “buck-boost” regulator, which is a switching regulator that can generate an output voltage that is opposite in polarity to the input, and a “flyback” regulator, which is a switching regulator that has multiple outputs and can generate output voltages that are less than or greater than the input.
FIG. 1 illustrates the startup characteristics of a conventional switching regulator under a sample small capacitor load (CLoad) and a sample large CLoad. In the example, both the small and large capacitor loads overshoot the target voltage of 1.4V as a result of excess current in the inductor. The small CLoad takes almost 160 microsecond (μs) to reach the target voltage and the large CLoad fails to reach the target voltage even at 200 μs. The overshoots and startup times are generally unacceptable.
To address the overshoot problem, some designers have incorporated a soft start into switching regulators. The soft start used increases a reference voltage provided to the switching regulator linearly so that excess current in the inductor is minimized. Depicted in FIGS. 2A-2B are the results of applying a linear soft start to the sample capacitor loads illustrated in FIG. 1.
In FIG. 2A, the linear soft start applied is sufficiently slow for the small CLoad, but not slow enough for the large CLoad. As a result, the large CLoad still overshoots the target voltage. In FIG. 2B, the linear soft start utilized is slow enough for the large CLoad, but the small CLoad then has to live with an unnecessarily long startup time.
Accordingly, there is a need for a soft start that optimizes startup time, minimizes overshoot, and is adaptable to load conditions. The present invention addresses such a need.